millimeter scales. It indicates that liquid molecules are long-range elastically correlated Consequently the thermal and density fluctuations are also elastically correlated, highlighting on the liquid state new mechanisms to consider to understand the
microfluidic scale. How to conciliate the low frequency shear elasticity and viscoelasticity theory when the scale goes down to the submillimeter scale? The polymer
viscoelasticity theory is founded on the predominance of the molecular dynamics
(major intrachain contribution). In contrast, the dynamics of simple liquids is
governed by intermolecular forces. How to conciliate intra- versus intermolecular
interactions when the polymer weight decreases down to simple liquids whose
dynamics are governed by intramolecular interactions? What are the underlying
assumptions and their limitations? This entry traces a brief history of the foundations
of the viscoelasticity theory, its empirical origin, and presents new developments
revealing that the conventional viscoelastic and viscous behaviors might be the
asymptotic part of a much broader dynamic response of the liquid state.
Keywords
Microfluidic · Unentangled and entangled polymer melts · Molecular liquids ·
Physiologic fluids · Low frequency · Solid-like properties
Definition
Dynamic mechanical relaxation aims at probing the response of a fluid to a mechanical stress by transmitting a shear stress via fluid/substrate contact in conditions as
close as possible to the equilibrium (linear conditions). The characteristic dynamic
variables are the viscoelastic moduli (shear elastic and viscous moduli). The
dynamic profile is built by varying the frequency in a range typically between
10
À3 and 10
3 Hz. Dynamic relaxation probes the very low-frequency properties,
while the majority of dynamic analysis techniques accesses MHz and GHz frequencies (NMR, inelastic scattering, Raman, Brillouin scattering, etc.).
The reliability of the dynamic relaxation measurement is entirely dependent on
the quality of the transmission of the stress via the sample via the fluid/substrate
interfacial forces (Fig. 1). This is the weak point of the technique. This entry shows
that the protocol of dynamic relaxation is improvable by optimizing the interaction
conditions between the sample and the substrate. Better measurement performances
are obtained in rheometry leading to the demonstration of elastic properties in the
liquid state previously neglected.
Introduction
Progresses in the dynamic characterization of fluids, polymer melts, or solutions are
essential given their implementation and the importance of their use in optimal
conditions. Among the three states of matter, the liquid state is certainly the most
poorly known, hardly modelled, and predictable. Rheology with the emergence of
250
L. Noirez
microfluidic scale. How to conciliate the low frequency shear elasticity and viscoelasticity theory when the scale goes down to the submillimeter scale? The polymer
viscoelasticity theory is founded on the predominance of the molecular dynamics
(major intrachain contribution). In contrast, the dynamics of simple liquids is
governed by intermolecular forces. How to conciliate intra- versus intermolecular
interactions when the polymer weight decreases down to simple liquids whose
dynamics are governed by intramolecular interactions? What are the underlying
assumptions and their limitations? This entry traces a brief history of the foundations
of the viscoelasticity theory, its empirical origin, and presents new developments
revealing that the conventional viscoelastic and viscous behaviors might be the
asymptotic part of a much broader dynamic response of the liquid state.
Keywords
Microfluidic · Unentangled and entangled polymer melts · Molecular liquids ·
Physiologic fluids · Low frequency · Solid-like properties
Definition
Dynamic mechanical relaxation aims at probing the response of a fluid to a mechanical stress by transmitting a shear stress via fluid/substrate contact in conditions as
close as possible to the equilibrium (linear conditions). The characteristic dynamic
variables are the viscoelastic moduli (shear elastic and viscous moduli). The
dynamic profile is built by varying the frequency in a range typically between
10
À3 and 10
3 Hz. Dynamic relaxation probes the very low-frequency properties,
while the majority of dynamic analysis techniques accesses MHz and GHz frequencies (NMR, inelastic scattering, Raman, Brillouin scattering, etc.).
The reliability of the dynamic relaxation measurement is entirely dependent on
the quality of the transmission of the stress via the sample via the fluid/substrate
interfacial forces (Fig. 1). This is the weak point of the technique. This entry shows
that the protocol of dynamic relaxation is improvable by optimizing the interaction
conditions between the sample and the substrate. Better measurement performances
are obtained in rheometry leading to the demonstration of elastic properties in the
liquid state previously neglected.
Introduction
Progresses in the dynamic characterization of fluids, polymer melts, or solutions are
essential given their implementation and the importance of their use in optimal
conditions. Among the three states of matter, the liquid state is certainly the most
poorly known, hardly modelled, and predictable. Rheology with the emergence of
250
L. Noirez